1. Field of the Invention
The present invention relates to a vertically aligned (VA) transflective liquid crystal display device, and more particularly, to a VA transflective liquid crystal display device with a single cell gap.
2. Description of the Related Art
Liquid crystal display (LCD) devices are widely used for portable televisions, notebook computers and other applications. Liquid crystal display devices are classified into transmissive devices using a backlight as a light source, and reflective devices using an external light source, such as sunlight or indoor lamp. It is difficult to conserve weight, volume, and power consumption of transmissive LCDs due to the power requirements of the backlight component. Reflective LCDs have the advantage of no backlight component, but cannot operate without an external light source.
An alternative to these types of LCDs is a transflective LCD device which can operate both reflectively and transmissively. Transflective LCD devices have a reflective electrode in a pixel region, wherein the reflective electrode has a transmissive portion. Thus, the transflective LCD device features lower power consumption than conventional transmissive LCD devices because no backlight component used when there is a bright external light. Further, the transflective LCD device has the advantage of operating as a transmissive LCD, using a backlight when required.
FIG. 1 is an exploded perspective view of a typical transflective LCD device. The transflective LCD device comprises upper and lower substrates 10 and 20 opposed to each other, and an interposed liquid crystal layer 50 therebetween. The upper substrate 10 acts as a color filter substrate and the lower substrate 20 an array substrate. In the upper substrate 10, black matrix 12 and color filter layer 14 including a plurality of red (R), green (G) and blue (B) color filters are formed. That is, the black matrix 12 surrounds each color filter, in the shape of an array matrix. Also on the upper substrate 10, a common electrode 16 is formed to cover the color filter layer 14 and the black matrix 12.
In the lower substrate 20, a TFT “T” acting as a switching device, is formed in the shape of an array matrix corresponding to the color filter layer 14. In addition, a plurality of crossing gate and data lines 26 and 28 are positioned such that each TFT is located near each intersection of the gate and data lines 26 and 28. Further on the lower substrate 20, a plurality of pixel regions (P) are defined by the gate and data lines 26 and 28. Each pixel region P has a pixel electrode 22 comprising a transparent portion 22a and an opaque portion 22b. The transparent portion 22a comprises a transparent conductive material, such as ITO (indium tin oxide) or IZO (indium zinc oxide), and the opaque portion 22b comprises a metal having high reflectivity, such as Al (aluminum) or Ag (silver).
FIG. 2, a sectional view of a conventional transflective LCD device, illustrates the operation thereof. As shown in FIG. 2, the conventional transflective LCD device comprises a lower substrate 200, an upper substrate 260 and an interposed liquid crystal layer 230. The upper substrate 260 comprises a common electrode 240 and a color filter 250 formed thereon. The lower substrate 200 comprises an insulating layer 210 and a pixel electrode 220 formed thereon, wherein the pixel electrode 220 comprises an opaque portion 222 and a transparent portion 224. The opaque portion 222 of the pixel electrode 220 can be an aluminum layer, and the transparent portion 224 of the pixel electrode 220 can be an ITO (indium tin oxide) layer. The opaque portion 222 reflects ambient light 270, while the transparent portion 224 transmits light 280 from a backlight device (not shown) disposed on the exterior of the lower substrate 200. Also, there is a drop between the opaque portion 222 and the transparent portion 224. The liquid crystal layer 230 is interposed between the lower and upper substrates 200 and 260. In FIG. 2, the liquid crystal layer 230 comprises dual cell. gaps. Generally, the material of the liquid crystal layer 230 comprises a twisted nematic (TN) type liquid crystal. Thus, the transflective LCD device is operable in both reflective and transmissive modes.
In U.S. Pat. No. 5,136,407, Clerc discloses avertically aligned LCD device. The LCD device has two groups of mutually crossing parallel electrodes sandwiching a liquid crystal layer, wherein the electrodes of one group comprise an aperture at each electrode intersection along the direction of and centrally at the electrode of the other group. The electric field at the aperture portion is constantly angled to a predetermined direction to present uniformly wide stable display areas. This method is usually applied to widen the viewing angle of the LCD, featuring slits separated by the same distance and utilizing liquid crystal molecules with negative dielectric anisotropy.
The conventional structure of slits between electrodes, nevertheless, is not presently applied to the transflective LCD device. Moreover, when the transflective LCD device uses the conventional method with equal spacing between slits, display brightness differs dramatically between the transmissive region and the reflective region. That is, the conventional configuration cannot achieve maximum light efficiency in both transmissive and reflective modes in the transflective LCD device.